Methods and systems for transmission of multiple modulated signals over wireless networks

ABSTRACT

A method and apparatus for requesting and allocating bandwidth in a broadband wireless communication system. The method and apparatus includes a combination of techniques that allow a plurality of CPEs to communicate their bandwidth request messages to respective base stations. One technique includes a “polling” method whereby a base station polls CPEs individually or in groups and allocates bandwidth specifically for the purpose of allowing the CPEs to respond with bandwidth requests. The polling of the CPEs by the base station may be in response to a CPE setting a “poll-me bit” or, alternatively, it may be periodic. Another technique comprises “piggybacking” bandwidth requests on bandwidth already allocated to a CPE. Currently active CPEs request bandwidth using unused portions of uplink bandwidth that is already allocated to the CPE. The CPE is responsible for distributing the allocated uplink bandwidth in a manner that accommodates the services provided by the CPE.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/523,573, filed on Oct. 24, 2014, and U.S. patent application Ser. No.14/523,755, filed on Oct. 24, 2014, which are a continuation of U.S.patent application Ser. No. 14/338,103, filed on Jul. 22, 2014, which isa continuation of U.S. patent application Ser. No. 14/170,271, filed onJan. 31, 2014, which is a divisional of U.S. patent application Ser. No.14/139,159, filed Dec. 23, 2013, which is a divisional of U.S. patentapplication Ser. No. 13/089,075, filed Apr. 18, 2011, now U.S. Pat. No.8,654,664, which is a divisional of U.S. patent application Ser. No.12/645,937, filed Dec. 23, 2009, now U.S. Pat. No. 8,315,640, which is acontinuation of U.S. patent application Ser. No. 11/170,392, filed Jun.29, 2005, now U.S. Pat. No. 8,189,514, which is a continuation of U.S.patent application Ser. No. 09/859,561, filed May 16, 2001, now U.S.Pat. No. 6,956,834, which is a continuation of U.S. patent applicationSer. No. 09/316,518, filed May 21, 1999, now U.S. Pat. No. 6,925,068,the disclosures of which are all incorporated herein by reference intheir entirety. U.S. patent application Ser. No. 14/338,103, filed onJul. 22, 2014, is also a continuation of U.S. patent application Ser.No. 13/649,986, filed Oct. 11, 2012, now U.S. Pat. No. 8,787,924, whichis a continuation of U.S. patent application Ser. No. 12/645,937, filedDec. 23, 2009, now U.S. Pat. No. 8,315,640, which is a continuation ofU.S. patent application Ser. No. 11/170,392, filed Jun. 29, 2005, nowU.S. Pat. No. 8,189,514, which is a continuation of U.S. patentapplication Ser. No. 09/859,561, filed May 16, 2001, now U.S. Pat. No.6,956,834, which is a continuation of U.S. patent application Ser. No.09/316,518, filed May 21, 1999, now U.S. Pat. No. 6,925,068, thedisclosures of which are incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to wireless communication systems, and moreparticularly to a method and apparatus for efficiently allocatingbandwidth between base stations and customer premises equipment in abroadband wireless communication system.

2. Description of Related Art

As described in U.S. Pat. No. 6,016,311, by Gilbert et al., issued Jan.18, 2000, entitled “Adaptive Time Division Duplexing Method andApparatus for Dynamic Bandwidth Allocation within a WirelessCommunication System,” hereby incorporated by reference, a wirelesscommunication system facilitates two-way communication between aplurality of subscriber radio stations or subscriber units (fixed andportable) and a fixed network infrastructure. Exemplary communicationsystems include mobile cellular telephone systems, personalcommunication systems (PCS), and cordless telephones. The key objectiveof these wireless communication systems is to provide communicationchannels on demand between the plurality of subscriber units and theirrespective base stations in order to connect a subscriber unit user withthe fixed network infrastructure (usually a wire-line system). In thewireless systems having multiple access schemes a time “frame” is usedas the basic information transmission unit. Each frame is sub-dividedinto a plurality of time slots. Some time slots are used for controlpurposes and some for information transfer. Subscriber units typicallycommunicate with the base station using a “duplexing” scheme thusallowing the exchange of information in both directions of connection.

Transmissions from the base station to the subscriber unit are commonlyreferred to as “downlink” transmissions. Transmissions from thesubscriber unit to the base station are commonly referred to as “uplink”transmissions. Depending upon the design criteria of a given system, theprior art wireless communication systems have typically used either timedivision duplexing (TDD) or frequency division duplexing (FDD) methodsto facilitate the exchange of information between the base station andthe subscriber units. Both the TDD and FDD duplexing schemes are wellknown in the art.

Recently, wideband or “broadband” wireless communications networks havebeen proposed for providing delivery of enhanced broadband services suchas voice, data and video services. The broadband wireless communicationsystem facilitates two-way communication between a plurality of basestations and a plurality of fixed subscriber stations or CustomerPremises Equipment (CPE). One exemplary broadband wireless communicationsystem is described in the co-pending application and is shown in theblock diagram of FIG. 1. As shown in FIG. 1, the exemplary broadbandwireless communication system 100 includes a plurality of cells 102.Each cell 102 contains an associated cell site 104 that primarilyincludes a base station 106 and an active antenna array 108. Each cell102 provides wireless connectivity between the cell's base station 106and a plurality of customer premises equipment (CPE) 110 positioned atfixed customer sites 112 throughout the coverage area of the cell 102.The users of the system 100 may include both residential and businesscustomers. Consequently, the users of the system have different andvarying usage and bandwidth requirement needs. Each cell may serviceseveral hundred or more residential and business CPEs.

The broadband wireless communication system 100 of FIG. 1 provides true“bandwidth-on-demand” to the plurality of CPEs 110. CPEs 110 requestbandwidth allocations from their respective base stations 106 based uponthe type and quality of services requested by the customers served bythe CPEs. Different broadband services have different bandwidth andlatency requirements. The type and quality of services available to thecustomers are variable and selectable. The amount of bandwidth dedicatedto a given service is determined by the information rate and the qualityof service required by that service (and also taking into accountbandwidth availability and other system parameters). For example,T1-type continuous data services typically require a great deal ofbandwidth having well-controlled delivery latency. Until terminated,these services require constant bandwidth allocation on each frame. Incontrast, certain types of data services such as Internet protocol dataservices (TCP/IP) are bursty, often idle (which at any one instantrequires zero bandwidth), and are relatively insensitive to delayvariations when active.

Due to the wide variety of CPE service requirements, and due to thelarge number of CPEs serviced by any one base station, the bandwidthallocation process in a broadband wireless communication system such asthat shown in FIG. 1 can become burdensome and complex. This isespecially true with regard to the allocation of uplink bandwidth. Basestations do not have a priori information regarding the bandwidth orquality of services that a selected CPE will require at any given time.Consequently, requests for changes to the uplink bandwidth allocationare necessarily frequent and varying. Due to this volatility in theuplink bandwidth requirements, the many CPEs serviced by a selected basestation will need to frequently initiate bandwidth allocation requests.If uncontrolled, the bandwidth allocation requests will detrimentallyaffect system performance. If left unchecked, the bandwidth required toaccommodate CPE bandwidth allocation requests will becomedisproportionately high in comparison with the bandwidth allocated forthe transmission of substantive traffic data. Thus, the communicationsystem bandwidth available to provide broadband services will bedisadvantageously reduced.

Therefore, a need exists for a method and apparatus that can dynamicallyand efficiently allocate bandwidth in a broadband wireless communicationsystem. The method and apparatus should be responsive to the needs of aparticular communication link. The bandwidth needs may vary due toseveral factors, including the type of service provided over the linkand the user type. The bandwidth allocation method and apparatus shouldbe efficient in terms of the amount of system bandwidth consumed by theactual bandwidth request and allocation process. That is, the pluralityof bandwidth requests generated by the CPE should consume a minimumpercentage of available uplink bandwidth. In addition, the bandwidthallocation method and apparatus should respond to bandwidth requests ina timely manner. Bandwidth should be allocated to high priority servicesin a sufficiently short time frame to maintain the quality of servicespecified by the CPE. Further, the bandwidth allocation method andapparatus should be capable of processing an arbitrarily large number ofbandwidth allocation requests from a relatively large number of CPEs.For example, in the system shown in FIG. 1, as many as one hundred CPEsmay be allowed to be simultaneously active, coordinating theirtransmissions on the uplink. Furthermore, the system can accommodateapproximately one thousand CPEs on the physical channel. Therefore, theneed exists for a bandwidth allocation method and apparatus that canprocess and respond to the bandwidth allocation requests generated by alarge number of CPEs.

Some prior art systems have attempted to solve bandwidth allocationrequirements in a system having a shared system resource by maintaininglogical queues associated with the various data sources requiring accessto the shared system resource. Such a prior art system is taught byKarol et al., in U.S. Pat. No. 5,675,573, that issued on Oct. 7, 1997.More specifically, Karol et al. teach a bandwidth allocation system thatallows packets or cells within traffic flows from different sources thatare contending for access to a shared processing fabric to get access tothat fabric in an order that is determined primarily on individualguaranteed bandwidth requirements associated with each traffic flow. Inaddition, the system taught by Karol et al. allow the different sourcesto gain access to the shared processing fabric in an order determinedsecondarily on overall system criteria, such as a time of arrival, ordue date of packets or cells within the traffic flows. Packets or cellsof data from each data source (such as a bandwidth requesting device)are queued in separate logical buffers while they await access to theprocessing fabric.

A need exits for a bandwidth allocation method and apparatus forefficiently processing and responding to bandwidth allocation requests.The bandwidth allocation method and apparatus should accommodate anarbitrarily large number of CPEs generating frequent and varyingbandwidth allocation requests on the uplink of a wireless communicationsystem. Such a bandwidth allocation method and apparatus should beefficient in terms of the amount of bandwidth consumed by the bandwidthrequest control messages exchanged between the plurality of basestations and the plurality of CPEs. In addition, the bandwidthallocation method and apparatus should respond to the bandwidthallocation requests in a timely and accurate manner. The bandwidthallocation method and apparatus should also be able to process anarbitrarily large number of bandwidth allocation requests generated by arelatively large number of CPEs. The present invention provides such abandwidth allocation method and apparatus.

SUMMARY OF THE INVENTION

The present invention is a novel method and apparatus for requesting andallocating bandwidth in a broadband wireless communication system. Themethod and apparatus reduces the amount of bandwidth that must beallocated for bandwidth request and bandwidth allocation purposes. Theopportunities for allowing a CPE to request bandwidth are very tightlycontrolled in accordance with the present invention. The presentinvention utilizes a combination of a number of bandwidth request andallocation techniques to control the bandwidth request process. Thereare a number of means by which a CPE can transmit a bandwidth requestmessage to an associated base station.

One such means uses a “polling” technique whereby a base station pollsone or more CPEs and allocates bandwidth specifically for the purpose ofallowing the CPEs to respond with a bandwidth request. The polling ofthe CPEs by the base station may be in response to a CPE setting a“poll-me bit” or, alternatively, it may be periodic. In accordance withthe present invention, periodic polls may be made to individual CPEs, togroups of CPEs, or to every CPE on a physical channel. When individuallypolling a CPE, the base station polls an individual CPE by allocatinguplink bandwidth in an uplink sub-frame map to allow the CPE to respondwith a bandwidth request. Similarly, in group polling, the base stationpolls several CPEs by allocating uplink bandwidth in the uplinksub-frame map to allow the CPEs to respond with a bandwidth request. TheCPEs must contend for the allocated bandwidth if collisions occur.Bandwidth allocations are not in the form of an explicit message that iscommunicated by the base station to the CPEs, but rather the bandwidthallocations are transmitted implicitly by allocating bandwidth in theuplink sub-frame map.

Another means used by the present invention in reducing bandwidthconsumed by the bandwidth request messages is the technique of“piggybacking” bandwidth requests on bandwidth already allocated to aCPE. In accordance with this technique, currently active CPEs requestbandwidth using previously unused portions of uplink bandwidth that isalready allocated to the CPE. Alternatively, the bandwidth requests canbe piggybacked on uplink bandwidth already allocated and currently beingused by a data service. In accordance with this alternative, the CPE“steals” bandwidth already allocated for a data connection by insertingbandwidth requests in time slots previously used for data.

The CPE is responsible for distributing the allocated uplink bandwidthin a manner that accommodates the services provided by the CPE. The CPEis free to use the uplink bandwidth that was allocated to it in a mannerthat is different than that originally requested or granted by the basestation. The CPE advantageously determines which services to givebandwidth to and which services must wait for subsequent bandwidthrequests. One advantage of having the CPE determine how to distributeits allocated bandwidth is that it relieves the base station fromperforming this task. In addition, the communication overhead that isrequired by having the base station instruct the CPE how to distributeits allocated bandwidth is eliminated. By using a combination ofbandwidth allocation techniques, the present invention advantageouslymakes use of the efficiency benefits associated with each technique.

The base station media access control (“MAC”) allocates availablebandwidth on a physical channel on the uplink and the downlink. Withinthe uplink and downlink sub-frames, the base station MAC allocates theavailable bandwidth between the various services depending upon thepriorities and rules imposed by their quality of service (“QoS”). Thebase station MAC maintains a set of queues for each physical channelthat it serves. Within each physical channel queue set, the base stationmaintains a queue for each QoS. The queues hold data that is ready to betransmitted to the CPEs present on the physical channel. The basestation higher MAC control layers are free to implement any convenientfairness or traffic shaping algorithms regarding the sharing of accessbetween connections at the same QoS, without impacting the base stationlower MAC control layers. In determining the amount of bandwidth toallocate at a particular QoS for a particular CPE, the base stationtakes into account the QoS, modulation, and the fairness criteria usedto keep an individual CPE from using up all available bandwidth. In oneembodiment, the base station attempts to balance the uplink/downlinkbandwidth allocations using an adaptive time-division duplexingtechnique (ATDD).

The uplink bandwidth allocation method is very similar to the downlinkbandwidth allocation except that, rather than being maintained by thebase station, the data queues are distributed across and maintained byeach individual CPE. Rather than check the queue status directly, thebase station preferably receives requests for bandwidth from the CPEsusing the techniques described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a broadband wireless communication system adapted for usewith the present invention.

FIG. 2 shows a TDD frame and multi-frame structure that can be used bythe communication system of FIG. 1 in practicing the present invention.

FIG. 3 shows an example of a downlink sub-frame that can be used by thebase stations to transmit information to the plurality of CPEs in thewireless communication of FIG. 1.

FIG. 4 shows an exemplary uplink sub-frame that is adapted for use withthe present bandwidth allocation invention.

FIG. 5 is a flow diagram showing the information exchange sequence usedin practicing the individual polling technique of the present invention.

FIG. 6 is a flow diagram showing the individual polling technique of thepresent invention.

FIG. 7 shows an exemplary uplink sub-frame map that is used tofacilitate the present multicast/broadcast bandwidth allocationtechnique.

FIG. 8 is a flow diagram showing the multicast and broadcast pollingtechnique of the present invention.

FIG. 9 is a flow diagram showing use of a “poll-me” to stimulate pollingof a CPE in accordance with the present invention.

FIG. 10 shows the message sequence that is used by the present inventionin requesting polls using the “poll-me” bit.

FIG. 11 is a flow diagram showing the bandwidth request piggybackingprocess of the present invention.

FIG. 12 shows the downlink bandwidth allocation method used by thepresent invention.

FIG. 13 shows the uplink bandwidth allocation method used by the presentinvention.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION OF THE INVENTION

Throughout this description, the preferred embodiment and examples shownshould be considered as exemplars, rather than as limitations on thepresent invention.

The preferred embodiment of the present invention is a method andapparatus for allocating bandwidth in a broadband wireless communicationsystem. One very important performance criterion of a broadband wirelesscommunication system, and any communication system for that matterhaving a physical communication medium shared by a plurality of users,is how efficiently the system uses the physical medium. Because wirelesscommunication systems are shared-medium communication networks, accessand transmission by subscribers to the network must be controlled. Inwireless communication systems a Media Access Control (“MAC”) protocoltypically controls user accesses to the physical medium. The MACdetermines when subscribers are allowed to transmit on the physicalmedium. In addition, if contentions are permitted, the MAC controls thecontention process and resolves any collisions that occur.

In the system shown in FIG. 1, the MAC executed by software present inthe base stations 106 (in some embodiments, the software may execute onprocessors both in the base stations and the CPE) control thetransmission time for all of the CPEs 110. The base stations 106 receiverequests for transmission rights and grant these requests within thetime available taking into account the priorities, service types,quality of service and other factors associated with the CPEs 110. Asdescribed above in the background of the invention, the servicesprovided by the CPEs 110 TDM information such as voice trunks from aPBX. At the other end of the service spectrum, the CPEs may uplinkbursty yet delay-tolerant computer data for communication with thewell-known World Wide Web or Internet.

The base station MAC maps and allocates bandwidth for both the uplinkand downlink communication links. These maps are developed andmaintained by the base station and are referred to as the UplinkSub-frame Maps and Downlink Sub-frame Maps. The MAC must allocatesufficient bandwidth to accommodate the bandwidth requirements imposedby high priority constant bit rate (CBR) services such as T1, E1 andsimilar constant bit rate services. In addition, the MAC must allocatethe remaining system bandwidth across the lower priority services suchas Internet Protocol (IP) data services. The MAC distributes bandwidthamong these lower priority services using various QoS dependenttechniques such as fair-weighted queuing and round-robin queuing.

The downlink of the communication system shown in FIG. 1 operates on apoint-to-multi-point basis (i.e., from the base station 106 to theplurality of CPEs 110). As described in U.S. Pat. No. 6,016,311, byGilbert et al., issued Jan. 18, 2000, entitled “Adaptive Time DivisionDuplexing Method and Apparatus for Dynamic Bandwidth Allocation within aWireless Communication System,” the central base station 106 includes asectored active antenna array 108 which is capable of simultaneouslytransmitting to several sectors. In one embodiment of the system 100,the active antenna array 108 transmits to six independent sectorssimultaneously. Within a given frequency channel and antenna sector, allstations receive the same transmission. The base station is the onlytransmitter operating in the downlink direction, hence it transmitswithout having to coordinate with other base stations, except for theoverall time-division duplexing that divides time into upstream (uplink)and downstream (downlink) transmission periods. The base stationbroadcasts to all of the CPEs in a sector (and frequency). The CPEsmonitor the addresses in the received messages and retain only thoseaddressed to them.

The CPEs 110 share the uplink on a demand basis that is controlled bythe base station MAC. Depending upon the class of service utilized by aCPE, the base station may issue a selected CPE continuing rights totransmit on the uplink, or the right to transmit may be granted by abase station after receipt of a request from the CPE. In addition toindividually addressed messages, messages may also be sent by the basestation to multicast groups (control messages and video distribution areexamples of multicast applications) as well as broadcast to all CPEs.

Within each sector, in accordance with the present invention, CPEs mustadhere to a transmission protocol that minimizes contention between CPEsand enables the service to be tailored to the delay and bandwidthrequirements of each user application. As described below in moredetail, this transmission protocol is accomplished through the use of apolling mechanism, with contention procedures used as a backup mechanismshould unusual conditions render the polling of all CPEs unfeasible inlight of given delay and response-time constraints. Contentionmechanisms can also be used to avoid individually polling CPEs that areinactive for long time periods. The polling techniques provided by thepresent inventive method and apparatus simplifies the access process andguarantees that service applications receive bandwidth allocation on adeterministic basis if required. In general, data service applicationsare relatively delay-tolerant. In contrast, real-time serviceapplications such as voice and video services require that bandwidthallocations be made in a timely manner and in adherence to verytightly-controlled schedules.

Frame Maps—Uplink and Downlink Sub-Frame Mappings

In one preferred embodiment of the present invention, the base stations106 maintain sub-frame maps of the bandwidth allocated to the uplink anddownlink communication links. As described in U.S. Pat. No. 6,016,311,by Gilbert et al., issued Jan. 18, 2000, entitled “Adaptive TimeDivision Duplexing Method and Apparatus for Dynamic Bandwidth Allocationwithin a Wireless Communication System,” the uplink and downlink arepreferably multiplexed in a time-division duplex (or “TDD”) manner. Inone embodiment, a frame is defined as comprising N consecutive timeperiods or time slots (where N remains constant). In accordance withthis “frame-based” approach, the communication system dynamicallyconfigures the first N.sub.1 time slots (where N is greater than orequal to N.sub.1) for downlink transmissions only. The remaining N.sub.2time slots are dynamically configured for uplink transmissions only(where N.sub.2 equals N−N.sub.1). Under this TDD frame-based scheme, thedownlink sub-frame is preferably transmitted first and is prefixed withinformation that is necessary for frame synchronization.

FIG. 2 shows a TDD frame and multi-frame structure 200 that can be usedby a communication system (such as that shown in FIG. 1) in practicingthe present invention. As shown in FIG. 2, the TDD frame is subdividedinto a plurality of physical slots (PS) 204. In the embodiment shown inFIG. 2, the frame is one millisecond in duration and includes 800physical slots. Alternatively, the present invention can be used withframes having longer or shorter duration and with more or fewer PSs. Theavailable bandwidth is allocated by a base station in units of a certainpre-defined number of PSs. Some form of digital encoding, such as thewell-known Reed-Solomon encoding method, is performed on the digitalinformation over a pre-defined number of bit units referred to asinformation elements (PI). The modulation may vary within the frame anddetermines the number of PS (and therefore the amount of time) requiredto transmit a selected PI.

As described in U.S. Pat. No. 6,016,311, by Gilbert et al., issued Jan.18, 2000, entitled “Adaptive Time Division Duplexing Method andApparatus for Dynamic Bandwidth Allocation within a WirelessCommunication System,” in one embodiment of the broadband wirelesscommunication system shown in FIG. 1, the TDD framing is adaptive. Thatis, the number of PSs allocated to the downlink versus the uplink variesover time. The present bandwidth allocation method and apparatus can beused in both adaptive and fixed TDD systems using a frame andmulti-frame structure similar to that shown in FIG. 2. As shown in FIG.2, to aid periodic functions, multiple frames 202 are grouped intomulti-frames 206, and multiple multi-frames 206 are grouped intohyper-frames 208. In one embodiment, each multi-frame 206 comprises twoframes 202, and each hyper-frame comprises twenty-two multi-frames 206.Other frame, multi-frame and hyper-frame structures can be used with thepresent invention. For example, in another embodiment of the presentinvention, each multi-frame 206 comprises sixteen frames 202, and eachhyper-frame comprises thirty-two multi-frames 206. Exemplary downlinkand uplink sub-frames used to in practicing the present invention areshown respectively in FIGS. 3 and 4.

Downlink Sub-Frame Map

FIG. 3 shows one example of a downlink sub-frame 300 that can be used bythe base stations 106 to transmit information to the plurality of CPEs110. The base station preferably maintains a downlink sub-frame map thatreflects the downlink bandwidth allocation. The downlink sub-frame 300preferably comprises a frame control header 302, a plurality of downlinkdata PSs 304 grouped by modulation type (e.g., PS 304 data modulatedusing a QAM-4 modulation scheme, PS 304′ data modulated using QAM-16,etc.) and possibly separated by associated modulation transition gaps(MTGs) 306 used to separate differently modulated data, and atransmit/receive transition gap 308. In any selected downlink sub-frameany one or more of the differently modulated data blocks may be absent.In one embodiment, modulation transition gaps (MTGs) 306 are 0 PS induration. As shown in FIG. 3, the frame control header 302 contains apreamble 310 used by the physical protocol layer (or PHY) forsynchronization and equalization purposes. The frame control header 302also includes control sections for both the PHY (312) and the MAC (314).

The downlink data PSs are used for transmitting data and controlmessages to the CPEs 110. This data is preferably encoded (using aReed-Solomon encoding scheme for example) and transmitted at the currentoperating modulation used by the selected CPE. Data is preferablytransmitted in a pre-defined modulation sequence: such as QAM-4,followed by QAM-16, followed by QAM-64. The modulation transition gaps306 contain preambles and are used to separate the modulations. The PHYControl portion 312 of the frame control header 302 preferably containsa broadcast message indicating the identity of the PS 304 at which themodulation scheme changes. Finally, as shown in FIG. 3, the Tx/Rxtransition gap 308 separates the downlink sub-frame from the uplinksub-frame which is described in more detail below.

Uplink Sub-Frame Map

FIG. 4 shows one example of an uplink sub-frame 400 that is adapted foruse with the present bandwidth allocation invention. In accordance withthe present bandwidth allocation method and apparatus, the CPEs 110(FIG. 1) use the uplink sub-frame 400 to transmit information (includingbandwidth requests) to their associated base stations 106. As shown inFIG. 4, there are three main classes of MAC control messages that aretransmitted by the CPEs 110 during the uplink frame: (1) those that aretransmitted in contention slots reserved for CPE registration(Registration Contention Slots 402); (2) those that are transmitted incontention slots reserved for responses to multicast and broadcast pollsfor bandwidth allocation (Bandwidth Request Contention Slots 404); andthose that are transmitted in bandwidth specifically allocated toindividual CPEs (CPE Scheduled Data Slots 406).

The bandwidth allocated for contention slots (i.e., the contention slots402 and 404) is grouped together and is transmitted using apre-determined modulation scheme. For example, in the embodiment shownin FIG. 4 the contention slots 402 and 404 are transmitted using a QAM-4modulation. The remaining bandwidth is grouped by CPE. During itsscheduled bandwidth, a CPE 110 transmits with a fixed modulation that isdetermined by the effects of environmental factors on transmissionbetween that CPE 110 and its associated base station 106. The downlinksub-frame 400 includes a plurality of CPE transition gaps (CTGs) 408that serve a similar function to the modulation transition gaps (MTGs)306 described above with reference to FIG. 3. That is, the CTGs 408separate the transmissions from the various CPEs 110 during the uplinksub-frame. In one embodiment, the CTGs 408 are 2 physical slots induration. A transmitting CPE preferably transmits a 1 PS preamble duringthe second PS of the CTG 408 thereby allowing the base station tosynchronize to the new CPE 110. Multiple CPEs 110 may transmit in theregistration contention period simultaneously resulting in collisions.When a collision occurs the base station may not respond.

By using the bandwidth allocation method and apparatus of the presentinvention, scheduled uplink traffic data is bandwidth allocated tospecific CPEs 110 for the transmission of control messages and servicesdata. The CPE scheduled data is ordered within the uplink sub-frame 400based upon the modulation scheme used by the CPEs 110. In accordancewith the present invention and in the manner described in detail below,bandwidth is requested by a CPE 110 and is subsequently granted by anassociated base station 106. All of the bandwidth allocated to aselected CPE within a given TDD frame (or alternatively an adaptive TDDframe, as the case may be) is grouped into a contiguous CPE scheduleddata block 406. The physical slots allocated for the CTGs 408 areincluded in the bandwidth allocation to a selected CPE 110 in the basestation uplink sub-frame map.

In addition to the bandwidth that is allocated for the transmission ofthe various types of broadband services (i.e., the bandwidth allocatedfor the CPE scheduled data slots 406), and the bandwidth allocated forCPE registration contention slots, bandwidth must also be allocated bythe base station MAC for control messages such as requests foradditional bandwidth allocations. As described in more detail below, inaccordance with the present invention, CPEs 110 request changes to theirbandwidth allocations by making bandwidth requests of their associatedbase stations 106. The present inventive method and apparatus reducesthe amount of bandwidth that must be set aside for these bandwidthallocation requests. In accordance with the present invention, theopportunities for requesting bandwidth are very tightly controlled. Thepresent invention advantageously utilizes a combination of a number oftechniques to tightly control the bandwidth request process. There are anumber of means by which a CPE can transmit a bandwidth request messageto its associated base station.

For example, one such means uses a “polling” technique whereby a basestation polls one or more CPEs and allocates bandwidth specifically forthe purpose of allowing the CPE(s) to transmit bandwidth requests. Inaccordance with this method, the polling of CPEs by the base station maybe in response to a CPE setting a “poll-me bit” in an upstream directionor it may be periodic. In accordance with the present invention,periodic polls may be made to individual CPEs (referred to as“reservation-based” polling), to groups of CPEs (“multicast” polling),or to every CPE on a physical channel (“broadcast” polling). Inreservation-based polling, the base station polls an individual CPE andthen allocates uplink bandwidth to allow the CPE to respond with abandwidth request. Similarly, in multicast and broadcast polling, thebase station polls several CPEs and then allocates uplink bandwidth toallow the CPEs to respond with a bandwidth request. However, the CPEsmust contend for the allocated bandwidth if collisions occur.Advantageously, neither the bandwidth polls nor the bandwidthallocations are in the form of explicit messages that are communicatedby the base station to the CPEs. Rather, the bandwidth polls compriseunsolicited grants of bandwidth sufficient for transmitting bandwidthrequests. Bandwidth allocations are implicit via bandwidth allocationsoccurring in the uplink sub-frame map. The polling techniques aredescribed in more detail below with reference to FIGS. 4-10.

As shown in FIG. 4, a portion of the uplink bandwidth may periodicallybe allocated for these bandwidth allocation or CPE connection requests.The uplink sub-frame 400 includes a plurality of bandwidth requestcontention slots 404. A CPE 110 must first be registered and achieveuplink synchronization with a base station before it is allowed torequest bandwidth allocation. Therefore there is no need to allow fortransmit time uncertainties in the length of the bandwidth requestcontention period. Consequently the bandwidth request contention periodmay be as small as a single PI, which, in one embodiment, at QAM-4requires 6 PS. As with the registration requests, if a collision occurs,the base station may not respond to the CPE. If, however, the basestation successfully receives a bandwidth request message from a CPE, itresponds by allocating the CPE additional scheduled data 406 bandwidthin the uplink sub-frame 400. The various polling techniques used by thepresent invention help to minimize the need to use the contention slots404. These techniques are described in more detail below.

Another means used by the present invention in reducing the bandwidthconsumed by the bandwidth request messages is the technique of“piggybacking” bandwidth requests on bandwidth already allocated to aCPE. In accordance with this technique, currently active CPEs requestbandwidth using previously unused portions of uplink bandwidth that isalready allocated to the CPE. The necessity of polling CPEs is therebyeliminated. In an alternative embodiment of the present invention,bandwidth requests are piggybacked on uplink bandwidth allocated andactively being used by a data service. In accordance with thisalternative, the CPE “steals” bandwidth already allocated for a dataconnection by inserting bandwidth requests in time slots previously usedfor data. The details of these piggybacking techniques are described inmore detail below with reference to FIG. 11.

Once a CPE is allocated bandwidth by the base station, the CPE, not thebase station, is responsible for using the uplink bandwidth in a mannerthat can accommodate the services provided by the CPE. The CPE is freeto use the uplink bandwidth that was allocated to it in a manner that isdifferent than originally requested or granted by the base station. Forexample, the service requirements presented to a selected CPE can changeafter the selected CPE requests bandwidth from its associated basestation. The CPE advantageously determines which services to givebandwidth to and which services must wait for subsequent bandwidthrequests. To this end, the CPE maintains a priority list of services.Those services having higher priority (e.g., those services having highquality of service demands) will be allocated bandwidth before thoseservices having lower priority (e.g., IP-type data services). If the CPEdoes not have sufficient bandwidth to meet its service requirements, theCPE will request additional bandwidth allocations by either setting itspoll-me bit or by piggybacking a bandwidth allocation request.

One advantage of having the CPE determine how to distribute itsallocated bandwidth is that it relieves the base station from performingthis task. In addition, the communication overhead that is required byhaving the base station instruct the CPE how to distribute its allocatedbandwidth is thereby eliminated, thus increasing usable systembandwidth. In addition, the CPE is in a much better position to respondto the varying uplink bandwidth allocation needs of high quality ofservice data services. Therefore, the CPE can better accommodate theneeds of these types of service requirements than can the base station.

The various techniques used by the present invention to enhance theefficiency of the bandwidth allocation request process are described inmore detail below in the sub-sections that follow. Although thesetechniques are described in separate sub-sections, the present inventivemethod and apparatus advantageously uses all of the techniques incombination to reduce the bandwidth consumed by the bandwidth allocationrequests.

Thus, the present invention advantageously makes use of the efficiencybenefits associated with each bandwidth allocation technique. Forexample, although an individual polling technique is beneficial withregard to the ability to provide fast response times to bandwidthallocation requests, it is relatively inefficient with regard to theamount of bandwidth consumed by the bandwidth allocation process. Incontrast, the group polling method is relatively efficient with regardto the bandwidth consumed by the bandwidth allocation process, but it isless efficient with regard to the ability to respond to bandwidthallocation requests. Use of a “poll-me” bit is relatively efficient whenconsidered from both the bandwidth consumption and response timeperspectives. In addition, the piggybacking technique further enhancesbandwidth consumption efficiency by using previously unused portions ofthe bandwidth to send the bandwidth allocation requests. In contrast tothe prior art approaches, the present invention advantageously uses allof these bandwidth allocation techniques in combination to maximizeefficiency.

Polling

In one embodiment of the broadband wireless system 100 of FIG. 1designed for use with the present invention, a CPE 110 is assigned adedicated connection identifier (ID) when the CPE 110 first registerswith the system 100. The ID is used when the base station 106 exchangescontrol messages with the plurality of CPEs 110. As described above,variations in bandwidth requirements (i.e., increases or decreases tobandwidth requirements) are necessary for all services transported bythe system 100 with the exception of uncompressible constant bit rate,or continuous grant (CG) services. The bandwidth requirements ofuncompressible CG services do not change between connectionestablishment and termination. The requirements of compressible CGservices, such as channelized-T1 services, may increase or decreasedepending on traffic.

In contrast, many of the data services facilitated by the system 100 ofFIG. 1 are bursty and delay-tolerant. Because bandwidth is provided tothese services on a demand assignment basis as needed these services arecommonly referred to as Demand-Assigned Multiple Access or “DAMA”services. When a CPE 110 needs to request bandwidth for a DAMA serviceit transmits a bandwidth request message to the base station 106. Thebandwidth request messages communicate the immediate bandwidthrequirements for the DAMA service. The bandwidth requirements can andtypically do vary over time. The quality of service or “QoS” for theDAMA connection is established when the CPE connection is initiallyestablished with the base station. Therefore, the base station has theability to access or “look-up” the QoS for any DAMA service that it iscurrently accommodating.

As described above, in accordance with the present invention, the CPEs110 have a number of different techniques available to them forcommunicating bandwidth request messages to their associated basestations. One such technique is by transmitting a bandwidth requestmessage in response to being polled by a base station. In accordancewith the polling technique taught by the present invention, the basestation allocates bandwidth to selected CPEs specifically for thepurpose of making bandwidth requests. The bandwidth allocations may beto individual CPEs or to groups of CPEs. As described in more detailbelow in the sub-section that describes the group polling technique,allocations to groups of CPEs define bandwidth request contention slotsthat are used in resolving bandwidth request collisions. Advantageously,the bandwidth allocations are not made in the form of explicit messages,but rather they are made in the form of bandwidth allocation increasesin the transmitted map describing the uplink sub-frame 400 (FIG. 4).Polling is performed on a per-CPE basis, bandwidth is requested on aper-connection-ID basis, and bandwidth is allocated on a per-CPE basis.These concepts are described in more detail below.

Reservation-Based Polling Technique (Individual Polling)

In accordance with the present inventive method and apparatus, when aCPE is polled individually, no explicit message is transmitted to pollthe selected CPE. Rather, the CPE is allocated bandwidth in the uplinksub-frame map that is sufficient to allow the CPE to respond with thebandwidth request. Specifically, the base station allocates bandwidth inthe CPE scheduled data block 406 (FIG. 4) for the selected CPE that issufficient to allow the selected CPE to respond with a bandwidth requestmessage. If the selected CPE does not require more bandwidth, it returnsa request for zero bytes. A zero byte request (rather than no request)is used in the individual polling process because explicit bandwidth fora reply is allocated.

In accordance with the present invention, only inactive CPEs and activeCPEs that explicitly request to be polled are eligible for individualpolling. Active CPEs that do not set their respective “poll-me” bits inthe MAC packet header will not be polled individually. Theserestrictions are imposed upon the bandwidth request process by thepresent invention and they advantageously save bandwidth compared withpolling all of the CPEs individually. In one embodiment of the presentinvention, active CPEs respond to polling using the modulation schemecurrently in use. However, inactive CPEs may respond using a QAM-4 orsimilarly robust modulation scheme to ensure that their transmission issufficiently robust to be detected by the base station even underadverse environmental conditions.

The present invention advantageously ensures timely responses torequests for more bandwidth for a constant bit rate service such as achannelized T1 service in which channels may be added or droppeddynamically. To ensure that the base station responds quickly torequests for more bandwidth for a constant bit rate service, the uplinkbandwidth allocated to a constant bit rate service that is not currentlyoperating at a maximum rate is made sufficiently large to accommodatethe service's current rate and a bandwidth request.

The information exchange sequence for individual polling is shown in theflow diagram of FIG. 5. As shown in FIG. 5, the base station preferablyhas several layers of control mechanisms or protocol stacks 502, 504 and506 that control, among other things, the bandwidth request andallocation process. The base station MAC is sub-divided into twosub-domains: (1) the HL-MAA MAC domain 504 and the LL-MAA Mac domain506. The LL-MAA MAC domain spans exactly a physical channel. Eachphysical channel requires an instance of the LL-MAA MAC domain. TheHL-MAA MAC domain spans multiple physical channels, typically all in thesame sector. A MAC domain comprises an HL-MAA MAC domain and the LL-MAAMAC domains associated with the physical channels within the HL-MAA MACdomain.

As shown in FIG. 5, the base station individually polls (as indicated bycontrol arrow 508) a CPE by allocating bandwidth sufficient for the CPEto respond with a bandwidth request message. This bandwidth is allocatedin the uplink sub-frame 400. If the CPE MAC 510 determines that there isdata to be sent for a selected connection k (typically determined bybeing instructed by a higher CPE control layer 512 via a control path514), then the CPE MAC control mechanism issues a bandwidth request 516to the base station MAC 506. If there is insufficient bandwidthavailable to the CPE 110 as determined by the base station's LL-MAA 506,the bandwidth request will not be granted. Else, the bandwidth requestwill be granted and this will be implicitly communicated to the CPE MAC510 by the base station allocating additional bandwidth to the CPE inthe uplink sub-frame 400. This is shown in FIG. 5 via the control path518. The CPE will then begin transmitting data to the base station overthe uplink using the bandwidth that has been allocated to it.

FIG. 6 is a flow diagram showing the individual polling technique 600provided by the present invention. As shown in FIG. 6, the method startsat decision STEP 602 to determine whether bandwidth is available for thepurpose of individually polling the CPEs. If no more bandwidth isavailable for individually polling the CPEs 110 then the method proceedsto STEP 604 and initiates a multicast or broadcast polling method. Thismulticast and broadcast polling method is described in detail in thesub-section below. However, if sufficient bandwidth is available for thepurpose of individually polling CPEs, the method proceeds to a decisionSTEP 606 whereat a determination is made whether there are any un-polledactive CPEs that have a “poll-me” bit set. If so, the method proceeds toa control point 608. If not, the method proceeds to a decision STEP 610whereat it determines whether there are any un-polled inactive CPEspresent. If so, the method proceeds to the control point 608. If not,the method proceeds to a control point 612.

The present inventive method proceeds from the control point 608 to STEP614 to individually poll the selected CPE. Thus, the method ensures thatonly un-polled active CPEs requesting more bandwidth (by setting theirrespective “poll-me” bits) and inactive CPEs are individually polled.This reduces bandwidth as compared with a polling method that wouldindividually poll all CPEs.

As shown in FIG. 6, at STEP 614 the base station initiates the pollingof the selected CPE and marks the CPE as polled. This is showndiagrammatically in FIG. 6 in the caption box 614′. The caption box 614′of FIG. 6 shows the downlink sub-frame map 300 described above in FIG.3. The MAC control portion 314 of the MAC frame control header 302preferably includes an uplink sub-frame map 400′. The uplink sub-framemap 400′ is communicated to the CPE MAC when the base station transmitsthis information to the CPE via the downlink. As shown in FIG. 6, andresponsive to the polling STEP 614, the base station MAC allocatesadditional bandwidth to the selected CPE (in FIG. 6 this CPE is referredto as CPE “k”) in the uplink. This increased bandwidth allocation iscommunicated to the CPE k via the uplink sub-frame map 400′. Thus, noadditional bandwidth is needed to respond to the need to poll theselected CPE.

As shown in FIG. 6, the method then returns to the decision STEP 602 todetermine whether there is more bandwidth available for individuallypolling the CPEs. When it is determined (at the decision STEPS 606 and610, respectively) that there are no active CPEs having a poll-me bitset and that there are no un-polled inactive CPEs present, the methodproceeds to a decision STEP 616. At the decision STEP 616, the methoddetermines whether any individual polls were performed. If not, themethod proceeds to a control point 618 and the method subsequentlyterminates at the termination step 620. However, if individual pollswere performed, the method proceeds to a STEP 622 to await theindividual bandwidth requests from the CPE that was polled (e.g., CPE“k”). As shown in the caption 622′ of FIG. 6, this bandwidth request 430is generated by the polled CPE (e.g., CPE “k”) during the CPE scheduleddata block 406 scheduled for the selected CPE in the uplink sub-frame400. In one embodiment, all data includes a header that indicates thetype of data being transmitted. For example, in this embodiment, controlmessages have associated CPE-unique connection identifiers that areassigned to them when the CPE registers. The structure of the controlmessages allows a base station to determine that a control message is abandwidth request.

As shown in FIG. 6, the method proceeds from STEP 622 to a decision STEP624 to determine whether any bandwidth requests were received. If not,the method terminates. However, if so, the method proceeds to a STEP 626whereat a bandwidth allocation method is initiated. As described in moredetail below, the base station uses a preferred bandwidth allocationmethod to allocate bandwidth to the requesting CPE. The bandwidthallocation is indicated to the CPE by making appropriate changes to theuplink sub-frame map 400′. The method then terminates at STEP 620.

Contention-Based Polling Technique (Multicast and Broadcast Polling)

As described above with reference to STEP 604 of the individual pollingmethod of FIG. 6, if there is not sufficient bandwidth available for thepurpose of individually polling the CPEs, the present invention may beused to poll the CPEs in multicast groups and a broadcast poll may beissued by the base station. Also, if there are more inactive CPEs thanthere is bandwidth available to individually poll them, some CPEs may bepolled in multicast groups and a broadcast poll may be issued.

In accordance with one embodiment of the invention, the addressing ofCPEs is preferably performed as follows: each CPE is assigned a uniquepermanent address (e.g., in one embodiment the CPE has a 48-bit address)that is used in the registration process; and each CPE is also given abasic connection ID (e.g., in one embodiment the CPE is given a 16-bitbasic connection ID and a 16-bit control connection ID during theregistration process). Each service that is provisioned for a selectedCPE is also assigned a connection ID. Connection IDs are generated bythe base station MAC (specifically, by the base station HL-MAA) and areunique across an HL-MAA MAC domain. The basic connection ID that isassigned when the CPE is registered with a base station is used by thebase station MAC and the CPE MAC to exchange MAC control messagesbetween the CPE and the base station. The control connection ID (alsoassigned during registration) is used by the base station and the CPE toexchange control and configuration information between the base stationand the CPE higher levels of control.

In accordance with one embodiment of the present invention, certainconnection IDs are reserved for multicast groups and broadcast messages.Of all of the addresses available a portion of them are preferablyreserved for multicast use. For example, in one embodiment of thepresent invention, if the four most-significant bits of the connectionID are set to logical ones (hex “Fxxxx”) the address is interpreted asbeing set aside for multicast use. In this embodiment, a total of 4Kdistinct multicast addresses are available. One example of such amulticast use is for the distribution of a video service. In onepreferred embodiment, the connection ID used to indicate a broadcast toall stations is (0xFFFF) (i.e., all 16 bits are set to a logical one).

Similar to the individual polling technique described above withreference to FIGS. 5 and 6, the multicast polling message is notexplicitly transmitted by the base station to the CPE. Rather, themulticast poll message is implicitly transmitted to the CPE when thebase station allocates bandwidth in the uplink sub-frame map. However,rather than associating allocated bandwidth with a CPE's basicconnection ID as done when performing an individual poll, the basestation associates the allocated bandwidth to a multicast or broadcastconnection ID. This multicast/broadcast bandwidth allocation is shown inthe multicast/broadcast uplink sub-frame map 400″ shown in FIG. 7. It isinstructive to compare the uplink sub-frame 400 (FIG. 4) used by thebase station when individual polling the CPEs with the uplink sub-framemap 400″ of FIG. 7. FIG. 7 shows the uplink sub-frame map which istransmitted in the MAC control portion of the downlink.

As shown in FIG. 7, the multicast/broadcast uplink sub-frame map 400″used by the present invention includes registration contention slots402″ that map the registration contention slots 402 of FIG. 4. However,rather than associating allocated bandwidth with a selected CPE's basicconnection ID, the allocated bandwidth is associated with a reservedregistration ID. As shown in FIG. 7, the uplink sub-frame map 400″preferably includes a plurality of multicast group bandwidth requestcontention slots 404″, 404′″, etc. The uplink sub-frame map 400″ alsoincludes broadcast bandwidth request contention slots 410. Finally,similar to the uplink sub-frame of FIG. 4, the uplink sub-frame map usedby the present invention to initiate multicast or broadcast pollsincludes a plurality of CPE scheduled data blocks 406″, 406′″, etc.,that are used to transport uplink traffic data.

In accordance with the present inventive method and apparatus, when apoll is directed to a multicast or broadcast connection ID, CPEsbelonging to the polled group request bandwidth using the bandwidthrequest contention slots (either the multicast contention slots for thegroup specified or the broadcast bandwidth request contention slots 410)allocated in the uplink sub-frame map 400″. In order to reduce thelikelihood of collisions only CPE's needing bandwidth are allowed toreply to multicast or broadcast polls. Zero-length bandwidth requestsare not allowed in the bandwidth request contention slots. In oneembodiment, CPEs transmit the bandwidth requests in the bandwidthrequest contention slots (e.g., contention slots 404) using QAM-4modulation. In this embodiment, the contention slots are sized to hold a1-PS preamble and a bandwidth request message. Due to physicalresolution characteristics, the message requires 1 PI (or 6 PS) usingQAM-4 modulation. In this embodiment, multiple bandwidth requestmessages from the same CPE fit in a single bandwidth request contentionslot without increasing the bandwidth utilization or the likelihood ofcollisions occurring. This allows the same CPE to make multiplebandwidth requests in the same slot.

If an error occurs when performing either a multicast or broadcast poll(such as the detection of an invalid connection ID) the base stationtransmits an explicit error message to the CPE. If the base station doesnot respond with either an error message or a bandwidth allocationwithin a predefined time period, the CPE will assume that a collisionoccurred. In this case the CPE uses a selected pre-defined contentionresolution process. For example, in one preferred embodiment, the CPEuses the well-known “slotted ALOHA” contention resolution process toback off and try at another contention opportunity.

Contention Resolution Process

Contention is necessary when there is insufficient time to poll all ofthe CPEs individually within a suitable interval. The base station isable to define contention periods both for multicast groups and also forall CPEs generally (i.e., broadcast). After CPE scheduled data, controlmessages, and polling are allowed for, the base station allocates allunused time in the upstream part of the TDD frame to contention, eitherfor bandwidth requests or for registration purposes. Typically thebandwidth request interval will be many PIs long (e.g., 1 PI=6 PS usingQAM-4 modulation). The CPEs must transmit their requests at a randomtime (on burst boundaries) within this interval to reduce the likelihoodof collisions occurring.

In accordance with the present invention, a CPE needing to transmit in arequest interval preferably randomly selects a PI within the interval,and makes a request in the associated starting PS. This randomizationminimizes the probability of collisions. A collision is presumed ifthere is no response from the base station to the request within apre-defined time period. If the base station does not respond within thepredefined time period the collision resolution process of the presentinvention is initiated.

One preferred embodiment of the present invention uses the followingresolution process: Assuming that the initial backoff parameter is i andthat the final backoff parameter is f,

1. On the first collision, the CPE waits a random interval between zeroand 2.sup.i contention opportunities and then tries again.

2. If another collision occurs, then the interval is doubled and the CPEtries again, repeating until the interval 2.sup.f is reached.

If the CPE is still unsuccessful, an error is reported to the systemcontroller and the contention process is aborted. Other contentionresolution mechanisms can be used to practice the present invention. Forexample, the well-known Ternary tree mechanism could be used to resolvecontentions.

FIG. 8 is a flowchart showing the multicast and broadcast polling method800 of the present invention. As shown in FIG. 8, the group pollingmethod 800 proceeds from an initial step 802 to a decision STEP 804whereat the method determines whether there is sufficient bandwidthavailable for multicast polls. If sufficient bandwidth is available formulticast polls, the method proceeds to a STEP 806 to poll the nextmulticast group in the MAC control portion 314 of the MAC frame controlheader 302. However, if there is insufficient bandwidth available toperform a multicast poll, the method proceeds to a decision STEP 808whereat the method determines whether there is sufficient availablebandwidth for performing a broadcast poll. If so, the method proceeds toa STEP 810. If not, the method proceeds to a decision STEP 812.

As shown in FIG. 8, at the STEP 810 a broadcast poll is initiated byplacing the broadcast poll in the MAC control portion 314 of the MACframe control header 302. Similar to the individual polling technique,the multicast poll message is implicitly transmitted to the CPE byallocating bandwidth in the uplink sub-frame map 400″. The allocatedbandwidth is associated with a multicast or broadcast connection ID.

At the decision STEP 812 the method determines whether a broadcast ormulticast poll was initiated. If so, the method proceeds to a STEP 814whereat the method monitors the appropriate bandwidth request contentionslots (e.g., as defined by the bandwidth contention slot descriptions404″, 404′″, and the broadcast bandwidth request contention slotdescriptions 410 of FIG. 7). If no broadcast or multicast poll wasinitiated, the method proceeds to control point 816 and subsequentlyterminates at a termination STEP 818.

The method proceeds from the monitoring STEP 814 to a decision STEP 820to determine whether valid (i.e., non-colliding) bandwidth requests weredetected. If no valid bandwidth requests were detected at STEP 820, themethod proceeds to the control point 816 and terminates at terminationSTEP 818. However, if the method detects valid bandwidth requests, themethod proceeds from STEP 820 to STEP 822. At STEP 822 the method uses aconvenient bandwidth allocation algorithm to allocate bandwidth to theCPE that requested bandwidth. The preferred bandwidth allocationalgorithm is described below in more detail with reference to FIGS.12-13. The bandwidth is allocated in the uplink sub-frame map 400″ asshown in FIG. 8.

Poll-Me Bit

As described above with reference to FIGS. 3-8, and in accordance withthe present invention, a currently active CPE sets a “poll-me” bit or a“priority poll-me” in a MAC packet in order to indicate to the basestation that it requires a change in bandwidth allocation. For example,in one embodiment of the present invention, a selected CPE requests apoll by setting a poll-me (“PM”) bit in the MAC header. Similarly, inaccordance with the present invention, a selected CPE sets a prioritypoll-me (“PPM”) bit in the MAC header in order to indicate that apriority poll is desired.

In order to reduce the bandwidth requirements associated withindividually polling every active CPE, the active CPEs are individuallypolled if and only if one of the poll-me bits is set by the CPE. Whenthe base station detects a request for polling (when the CPE sets itspoll-me bit), the individual polling technique shown in FIG. 9 isactivated in order to satisfy the request. The procedure by which a CPEstimulates a base station to poll the CPE is shown in FIG. 9. In analternative embodiment, multiple packets having “poll-me” bits setindicate that the CPE needs to make bandwidth allocation requests formultiple connections.

FIG. 9 is a flow chart that shows how the poll-me bit is used tostimulate polling in accordance with the present invention. As shown inFIG. 9, the method first determines at a decision STEP 902 whether thepiggybacking technique described in more detail below has beenexhausted. If not, the method proceeds to STEP 904 and attempts toperform “piggybacking” first. The method then proceeds to a STEP 906whereat the connection is set equal to a first connection. In thismanner, the poll-me bits are scanned for each connection within the CPE.The method shown in FIG. 9 then proceeds to a decision STEP 908 todetermine whether any bandwidth needs exist. If not, the method proceedsto a STEP 916 and scans for the next connection. If a bandwidth needexists, the method proceeds to a decision STEP 910. At STEP 910 themethod determines whether any more packets are available foraccommodating the poll-me bit. If not, the method terminates at the STEP910. However, if packets are available, the method proceeds to a STEP912 and sets a poll-me bit in an available packet.

FIG. 10 shows the message sequence that is used by the present inventionin requesting polls using the “poll-me” bit described above. As shown inFIG. 10 at data connection 930, the CPE initiates a polling sequence bysetting its associated poll-me bit in the MAC header. The base stationMAC responds via data message 932 by individually polling the selectedCPE. This response is made by allocating bandwidth to the selected CPEin the uplink sub-frame map as shown in FIG. 10. The selected CPEsubsequently responds with a bandwidth request as shown in communicationpath 934. In response to the CPE's bandwidth request, the base stationgrants bandwidth and allocates bandwidth to the CPE in the uplinksub-frame map as shown in communication path 936. The selected CPE thentransmits its data to the base station via an associated connectionlink.

“Piggybacking” Technique

As described above with reference to the present inventive method andapparatus, in order to further reduce overhead bandwidth necessary forthe bandwidth allocation process, currently active CPEs may “piggyback”a bandwidth request (or any other control message) on their currenttransmissions. The CPEs accomplish this piggybacking of bandwidth byusing unused bandwidth in TC/PHY packets of existing bandwidthallocations. The procedure for using excess bandwidth in this manner isshown in FIG. 11.

As shown in FIG. 11, the method initiates the piggybacking process atSTEP 950. The method proceeds to a decision STEP 952 to determinewhether the CPE requires additional bandwidth. If so, the methodproceeds to a decision STEP 954, if not, the method proceeds to atermination STEP 964 whereat the method terminates. At the decision STEP954 the method determines whether any unused bytes exist in the currentallocation. If so, the method proceeds to insert bandwidth requests intothe unused bytes at STEP 956. If not, the method proceeds to a decisionSTEP 958. At the decision STEP 958, the method determines whether anypackets at all are allocated to the CPE. If there are no packets foundat the decision STEP 958, the method proceeds to STEP 960. However, ifpackets are allocated, the method proceeds to a STEP 962 whereat the CPEsets its poll-me bit. The method then proceeds to the STEP 960 whereatthe CPE awaits polling by the associated base station. The method thenterminates at the STEP 964.

Bandwidth Allocation

As described above, the base station MAC is responsible for allocatingthe available bandwidth of a physical channel on the uplink and thedownlink. Within the uplink and downlink sub-frames, the base stationMAC scheduler allocates the available bandwidth between the variousservices depending upon the priorities and rules imposed by theirquality of service (QoS). Additionally, the higher control sub-layers ofthe base station MAC allocate across more than one physical channel.

Down Link Bandwidth Allocation One Embodiment

The downlink bandwidth is allocated as shown in FIG. 12. The basestation MAC maintains a set of queues for each physical channel that itserves. Within each physical channel queue set, the base stationmaintains a queue for each QoS. The queues hold data that is ready to betransmitted to the CPEs present on the physical channel. The higherlayers of the base station protocol stack are responsible for the orderin which data is place in the individual queues. The base station highercontrol layers are free to implement any convenient fairness or trafficshaping algorithms regarding the sharing of access between connectionsat the same QoS, without impacting the base station lower MAC controllayers. Once data is present in the queues it is the responsibility ofthe base station lower levels of control (e.g., the BS LL-MAA of FIGS. 5and 10) to allocate bandwidth based on the QoS.

In one embodiment of the present invention, in determining the amount ofbandwidth to allocate at a particular QoS for a particular CPE, the basestation takes into account the QoS, modulation, and the fairnesscriteria used to keep an individual CPE from using up all availablebandwidth. Bandwidth is preferably allocated in QoS order. If there is aqueue that cannot be transmitted entirely within a particular TDD frame,a QoS specific fairness algorithm, such as fair-weighted queuing, isused within that queue. Each connection is given a portion of theremaining available bandwidth based upon its relative weight. Thederivation of weights is QoS-dependant. For example, ATM traffic may beweighted based upon contractual bandwidth limits or guarantees, while IPconnections may all receive identical weights. Once the bandwidth isallocated the data is transmitted in a manner whereby the data is sortedby modulation type.

Uplink Bandwidth Allocation One Embodiment

The uplink bandwidth allocation method is very similar to the downlinkbandwidth allocation method described above with reference to FIG. 12.However, rather than being maintained by the base station, the dataqueues are distributed across and maintained by each individual CPE.Rather than check the queue status directly, the base station preferablyreceives requests for bandwidth from the CPEs using the techniquesdescribed above with reference to FIGS. 3-11. Using these bandwidthrequests, the base station reconstructs a logical picture of the stateof the CPE data queues. Based on this logical view of the set of queues,the base station allocates uplink bandwidth in the same way as itallocates downlink bandwidth. This uplink bandwidth allocation techniqueis shown in FIG. 13.

As described above, the bandwidth allocated to any selected CPE istransmitted to the selected CPE in the form of bandwidth being allocatedin the uplink sub-frame map. Starting at a point in the TDD, the uplinksub-frame map allocates a certain amount of bandwidth to the selectedCPE. The selected CPE then allocates this bandwidth across itsconnections. This allows the CPE to use the bandwidth in a differentmanner than requested if it receives higher priority data while awaitingthe bandwidth allocation. As described above, the bandwidth allocationsare in a constant state of change owing to the dynamic nature ofbandwidth requirements. Consequently, a selected CPE may receiveunsolicited modifications to the bandwidth granted on a frame-by-framebasis. If the selected CPE is allocated less bandwidth for a frame thanis necessary to transmit all waiting data, the CPE must use the QoSs andfairness algorithms to service its queues. The CPE may “steal” bandwidthfrom lower QoS connections to piggyback request for more bandwidth usingthe piggybacking technique described above. TDM connections not alreadyat maximum bandwidth are allocated enough extra bandwidth in the uplinkto piggyback a request for additional bandwidth.

QoS Specific Fairness Algorithms

Data for transmission on the uplink and the, downlink is preferablyqueued by quality of service (QoS) designations. The data is transmittedin order of a QoS queue priority as described above. As the queued datais transmitted, there may be a QoS queue for which there is insufficientbandwidth to transmit all queued data during the current TDD frame. Whenthis situation occurs, a QoS specific fairness algorithm is initiated toensure fair handling of the data queued at that QoS. There are 3 basicfairness algorithms that can be implemented: (1) Continuous Grant; (2)Fair-weighted queuing; and (3) Round Robin.

The MAC preferably does not police connections for bandwidth usage.Policing should be performed by higher control layers. The MAC assumesthat all pending data has met contractual restrictions and can betransmitted. Continuous Grant queues have the simplest fairnessalgorithm. All data in these queues must be sent every TDD frame.Insufficient bandwidth indicates an error in provisioning.

Fair Weighted Queuing

Fair weighted queuing requires that all connections at a given QoS havea weight, assigned to them to determine the percentage of the availablebandwidth they are eligible to receive. This weight value is preferablyderived from one of three data rate parameters, depending upon thecontractual parameters of the provisioned connection. These threeparameters are: (1) Data Pending; (2) Guaranteed Rate; and (3) AverageRate.

Real-time VBR connections are established as DAMA connections withfair-weighted queuing based upon data pending. For a QoS queue of thistype in a TDD frame having insufficient bandwidth to transmit all of thedata in the queue, a weight for each connection in the queue isdetermined. In one embodiment, this weight is the amount of data pendingfor the connection expressed as a percentage of the total data pendingin the queue. Because the amount of data pending is dynamic, the weightsfor these types of queues must be determined every TDD frame where thereis insufficient bandwidth to send all data in the affected queue.

For DAMA connections contracted at a guaranteed rate the weights arecalculated based on the guaranteed rate. In this case, the weightpreferably is expressed as a percentage of the total guaranteed rate ofall connections with data pending in the queue. Because the guaranteedrate is provisioned the weights need not be determined each TDD framewhere they are used. Rather, the weights for a queue are only determinedwhen there is a provisioning change (i.e., a new connection, a change inconnection parameters, or a connection termination) for one of theconnections in the queue.

For DAMA connections contracted at an average rate the weights arepreferably calculated based on the average rate. The weight is theaverage rate expressed as a percentage of the total average rate of allconnections with data pending in the queue. Because the average rate isprovisioned the weights need not be determined each TDD frame where theyare used. Rather, the weights for a queue are only recalculated whenthere is a provisioning change for one of the connections in the queue.

In all of the cases described above, the granularity of the bandwidthallocations may be too coarse to provide a perfect percentage-basedweighted allocation across the connections in the queue. This may resultin some queues not receiving any bandwidth in a particular TDD frame. Toensure that the occurrence of this condition is fairly distributedacross the connections in the queue, the connection that did not receivebandwidth is given priority the next time the insufficient bandwidthcondition exists for the queue. For queues with weights based uponguaranteed or average rates some connections may not have sufficientdata pending to use all of the bandwidth that they are entitled to basedupon their calculated weight. In these cases, the connection's unusedbandwidth is fairly distributed across the connections having excessdata pending.

Some QoSs require that data be aged. For queues at these QoSs there isan associated queue of one step higher priority. If data is nottransmitted by the provisioned aging parameter, the data is moved to thehigher QoS queue and given priority over newer data in the originalqueue regardless of the relative weights of the connections.

Round Robin

The Round Robin fairness algorithm is used for best effort connectionswhere all connections have equal weight. When insufficient bandwidthexists to transmit all data in the queue in a particular TDD frameconnections are allocated bandwidth in a round-robin fashion with eachconnection receiving a block of bandwidth up to a queue-specificmaximum. Connections that did not receive bandwidth are given priorityhe next time the insufficient bandwidth condition exists.

Bandwidth Allocation Algorithm

For each TDD frame, the base station allocates the downlink portion ofthe TDD frame and it performs an estimate of the uplink traffic toallocate uplink bandwidth to the CPEs. The CPEs individually allocatetheir allotted bandwidth across their pending data connections.

Base Station Downlink

As shown in FIG. 2, in one preferred embodiment of the presentinvention, based on the ATDD split (i.e., the percentage of bandwidthallocated to the uplink and downlink) the base station has some numberof the 800 PS in the TDD frame available for downlink transmissions. Thedownlink bandwidth allocation algorithm preferably proceeds as follows.

First, the base station allocates PSs to the PI for PHY Control andenough PSs for at least 1 PI for the MAC Control. The base stationpreferably performs uplink bandwidth allocation before downlinkbandwidth allocation in order to determine the number of PIs to allocatefor the MAC Control. In one preferred embodiment, the PHY Control andMAC Control are always sent using QAM-4 modulation.

For connections with downlink continuous grant data pending, the basestation determines the number of PIs required to transmit the data. Thisnumber is then converted to PSs as a function of the modulation used forthe CPE associated with each connection. For each remaining QoS or untilavailable bandwidth is entirely allocated, the base station determinesif there is enough bandwidth to satisfy the entire need of the QoSqueue. If so, the base station allocates the required bandwidth.Otherwise, if there is not enough bandwidth to satisfy the queue, thebase station implements the queue-specific fairness algorithm describedabove.

Base Station Uplink

In one preferred embodiment, based upon the ATDD split described abovewith reference to FIG. 2, the base station has a pre-determined numberof PSs in the TDD frame available for uplink transmissions. The basestation must maintain an estimate of the data and control messagespending at each QoS for the CPEs that it serves. The base stationestimates the data traffic based upon the bandwidth requests receivedfrom the CPEs and based upon an observation of actual data traffic. Thebase station estimates the uplink control message traffic based upon theprotocols currently engaged (i.e., connection establishment, “poll-me”bit usage, etc.) and based upon the base station's polling policy (i.e.,individual, multicast, and broadcast). The uplink bandwidth allocationalgorithm proceeds as follows.

For connections with uplink continuous grant data pending, the basestation preferably determines the number of PIs required to transmit thedata. This number is then converted to a number of PSs as determined bythe modulation used for the CPE associated with each connection.Continuous grant connections having a current bandwidth that is lessthan the maximum bandwidth are always allocated uplink bandwidth that isthe smaller of: 1) their maximum bandwidth or 2) their current bandwidthplus the bandwidth necessary to send a CG bandwidth change message.

For each remaining QoS, or until available bandwidth is entirelyallocated, the base station determines if there is bandwidth sufficientto satisfy the entire need of the QoS queue and it then allocates therequired bandwidth. Otherwise, if there is not bandwidth sufficient tosatisfy the queue, the base station implements the queue-specificfairness algorithm described above.

CPE Uplink

As described above, for each TDD frame, the CPEs are allocated a portionof the uplink sub-frame in which to transmit their respective data.Because the bandwidth requirements of the CPE may have changed since thebase station received the bandwidth request information that it used toallocate the uplink bandwidth, the CPEs themselves are responsible forallocating their allotted bandwidth based upon their current bandwidthrequirements. That is, the CPEs are not constrained to distributeallocated bandwidth to their data connections in the same manner thatthe CPE used in requesting the bandwidth from the base station. TheCPE's uplink bandwidth allocation algorithm preferably proceeds asfollows.

For connections having uplink continuous grant data pending, the CPEdetermines the number of PIs that are required to transmit the data.This number is then converted to a PS number based upon the modulationscheme used by the CPE. For each remaining QoS, or until availablebandwidth is entirely allocated, the CPE determines if there isbandwidth sufficient to satisfy the entire need of the QoS queue. If so,the CPE allocates the required bandwidth. Otherwise, if there is notbandwidth sufficient to satisfy the queue, the CPE implements thequeue-specific fairness algorithm described above.

SUMMARY

In summary, the bandwidth allocation method and apparatus of the presentinvention includes a powerful, highly efficient means for allocatingbandwidth in a broadband wireless communication system. The presentbandwidth allocation method and apparatus uses a combination ofindividual and group polling techniques, contention-based polling,piggybacking, and CPE-initiated techniques to efficiently allocatebandwidth in a communication system. Advantageously, only thosecurrently active CPEs (CPEs that currently have bandwidth allocationsassociated thereto) are permitted to request more bandwidth using eitherthe piggybacking or poll-me bit methods. In addition, the presentinvention saves bandwidth by implicitly informing the CPE of additionalbandwidth allocation. The base station implicitly informs the CPE ofadditional bandwidth allocation by allocating additional bandwidth tothe CPE in the uplink sub-frame map. Similarly, the base stationsimplicitly poll the CPEs by allocating bandwidth in the uplink to enablethe CPEs to respond to the poll with a bandwidth request.

In honoring the bandwidth requests, the base station builds andmaintains a logical queue of the data to be transmitted. The queues aredeveloped by the base stations based upon the QoS. In addition, the basestation allocates bandwidth based on a combination of QoS and a QoSunique fairness algorithm. The CPE itself, rather than the base station,distributes the allocated bandwidth to its services in any manner theCPE determines to be appropriate. Thus, the CPE can use its allocatedbandwidth in a manner that differs from the originally intended (andrequested) purpose.

A number of embodiments of the present invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, the present inventive method and apparatus can be used in anytype of communication, its use is not limited to a wirelesscommunication system. One such example is use of the invention in asatellite communication system. In such a communication system,satellites replace the base stations described above. In addition, theCPEs are not longer at fixed distances from the satellites. Therefore,it will be more difficult to schedule DAMA services for the CPEs.Alternatively, the present invention can be used in a wiredcommunication system. The only difference between the wired system andthe wireless system described above is that the channel characteristicsvary between the two. However, the bandwidth allocations do not changeas between the two types of systems. Accordingly, it is to be understoodthat the invention is not to be limited by the specific illustratedembodiment, but only by the scope of the appended claims.

1. A wireless cellular mobile unit operable to share an uplink to a base station with other wireless cellular mobile units in a wireless communication system, the wireless cellular mobile unit comprising: a transceiver operable to transmit a bandwidth request which identifies an amount of data awaiting transmission to the base station, receive an uplink allocation indication with current uplink (UL) bandwidth allocations for a plurality of wireless cellular mobile units, including the wireless cellular mobile unit, and identify in the UL allocation indication an UL bandwidth grant allocated to the wireless cellular mobile unit for data transmission in a current frame; and one or more processors having a Media Access Controller (MAC) operable to allocate the UL bandwidth grant among one or more UL connections that have data awaiting UL transmission from the wireless cellular mobile unit to the base station, based on a quality of service parameter.
 2. A wireless cellular mobile unit as claimed in claim 1, wherein the transceiver is further operable to transmit an explicit message to the base station indicating a requirement to be provided an allocation of UL bandwidth in which to transit the bandwidth request.
 3. A wireless cellular mobile unit as claimed in claim 1, wherein the MAC is operable to allocate the UL bandwidth grant among the one or more UL connections also based on the amount of data awaiting UL transmission for the one or more UL connections.
 4. A wireless cellular mobile unit as claimed in claim 1, wherein the bandwidth request specifies a requested amount of UL bandwidth in bandwidth units.
 5. A wireless cellular mobile unit as claimed in claim 1, wherein the transceiver is operable to receive the UL bandwidth grant in the UL frame allocation indication, without receiving an acknowledgement of receipt by the base station of the bandwidth request.
 6. A wireless cellular mobile unit as claimed in claim 1, wherein the transceiver is operable to transmit the bandwidth request within UL bandwidth already allocated for UL traffic.
 7. A wireless cellular mobile unit as claimed in claim 1, wherein the transceiver is operable to transmit the bandwidth request within the payload of a packet carrying UL traffic.
 8. A wireless cellular mobile unit as claimed in claim 1, wherein the transceiver is operable to transmit the bandwidth request within UL bandwidth specifically allocated to the wireless cellular mobile unit for the bandwidth request.
 9. A wireless cellular mobile unit as claimed in claim 1, wherein the transceiver is further operable to: receive a bandwidth request opportunity allocation indication; and transmit the bandwidth request using the bandwidth request opportunity.
 10. A wireless cellular mobile unit as claimed in claim 1, wherein the transceiver is operable to register the wireless cellular mobile unit with the base station, achieve uplink synchronization with the base station and establish communication between the wireless cellular mobile unit and the base station.
 11. A wireless cellular mobile unit operable to share an uplink to a base station with other wireless cellular mobile units in a wireless communication system, the wireless cellular mobile unit comprising: one or more processors having a Media Access Controller (MAC) operable to provide a bandwidth request indicating a requested amount of uplink (UL) bandwidth pertaining to one or more UL connections established at the wireless cellular mobile unit; and a transceiver operable to transmit to the base station a request for polling, receive from the base station a bandwidth request opportunity having an amount of UL bandwidth, transmit a bandwidth request within the amount of UL bandwidth, receive an UL bandwidth grant in response to the bandwidth request, and receive an allocation indication control message from the base station, which identifies the UL grant.
 12. A wireless cellular mobile unit as claimed in claim 11, wherein the request for polling is a poll-me message.
 13. A wireless cellular mobile unit operable to share an uplink to a base station with other wireless cellular mobile units in a wireless communication system, the wireless cellular mobile unit comprising: a transceiver operable to transmit a bandwidth request, and receive a control message identifying an uplink (UL) bandwidth grant allocated to the wireless cellular mobile unit for data transmission in a current frame; and one or more processors having a Media Access Controller (MAC) operable to allocate the UL bandwidth grant among one or more queues, wherein a queue of the one or more queues accumulates data with similar quality of service associated with one or more UL connections, the data accumulated in the queue awaiting transmission from the wireless cellular mobile unit to the base station.
 14. A wireless cellular mobile unit as claimed in claim 13, wherein the data accumulated in the one or more queues is scheduled for transmission based on a quality of service parameter.
 15. A wireless cellular mobile unit as claimed in claim 14, wherein the UL bandwidth grant is distributed among at least two UL connections that have data pending in the queue using one of a fair-weighted queuing and a round-robin queuing technique.
 16. A wireless cellular mobile unit as claimed in claim 13, wherein the bandwidth request identifies an amount of data awaiting transmission from the wireless cellular mobile unit to the base station.
 17. A wireless cellular mobile unit as claimed in claim 13, wherein the transceiver is further operable to transmit an explicit message to the base station indicating a requirement to be provided an allocation of UL bandwidth in which to transmit the bandwidth request 